-LRB- CNN -RRB- -- An ice jam on the Yukon River in Alaska sparked flooding in the city of Galena , where some 300 people have been evacuated , authorities said .

Most of the people who left their homes were being housed in either Ruby or Fairbanks , said Kerry Seifert , operations section chief at the Alaska Division of Homeland Security and Emergency Management .

Some are at shelters , while others were with friends and relatives .

`` We expect the flooding to become worse before the waters start to recede , '' said Alaska Gov. Sean Parnell , who surveyed the damage this week .

`` Ensuring the safety of those impacted by the flooding remains my top priority . ''

According to Seifert , the cause of the jam was a late break up of ice .

Colder temperatures meant there was no melting until a rapid warming put lots of water in the river basin .

A wall of ice got hung up at a steep curve in the river near Galena , he said .

Water appeared to be beginning to move around the sides of the ice Wednesday , Seifert said , which could be good news for people living in Galena .

When the jam breaks , however , downriver communities of Koyukuk and Nulato may be at risk .

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A wall of ice got hung up at a steep curve in the Yukon River

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Some 300 people are evacuated

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`` We expect the flooding to become worse before the waters start to recede , '' governor says